This competitive renewal project proposes to extend studies of the hypothalamic-pituitary-adrenal axis in fibromyalgia syndrome previously undertaken by the PI. Her initial data suggested reduced adrenocorticotropin (ACTH) and epinephrine responses to graded hypoglycemic challenge, and blunting of the normal diurnal cortisol rhythm in patients with fibromyalgia when compared to normal controls. The PI postulates that the decreased ACTH response to hypoglycemic challenge is the result of impaired CRH release, this also results in decreased sympathoadrenal response to hypoglycemia. The PI further proposes that the diurnal cortisol rhythm in patients with fibromyalgia is abnormal due to a shift in the circadian phase. In Specific Aim 1, the PI and her colleagues propose to assess hypothalamic CRH-pituitary ACTH activity at baseline and in response to three stimuli: hypoglycemia, metapyrone-induced glucocorticoid administration, and an immune stimulus with tetanus toxoid vaccine. In Specific Aim 2, sypathoadrenal responses to hypoglycemia, the cold pressor test, metapyrone vs. placebo will be compared in patients with fibromyalgia and controls. In Specific Aim 3, the circadian phase (measured by core body temperature and melatonin levels) will be compared in women with fibromyalgia and healthy controls. Additional studies of the relationship between disrupted sleep pattern and night-time secretion of ACTH and cortisol and cytokines are planned if the circadian phase is not shifted.